Federal law and that of some states allows a lower minimum wage for tipped employees. [1] So the financial delta for the restaurant may be bigger than that described.

Blame the powerful restaurateur lobby. [2]

[1] https://www.dol.gov/whd/state/tipped.htm

[2] http://www.npr.org/sections/thesalt/2016/02/02/464852535/for...